1. Field of the Invention
This invention relates to field-effect transistors.
2. Discussion of the Related Art
One of the most important electronic devices is the field-effect-transistor (FET). A FET has a source electrode, a drain electrode, and an active semiconductor channel for carrying a current between the source and drain electrodes. In the FET, the current flow in the active semiconductor channel is controlled through the channel conductivity. In particular, the FET includes a gate structure for producing an electric field to vary the conductivity of the active semiconductor channel. The gate structure includes a gate electrode and a gate dielectric for electrically insulating the gate electrode from the channel.
The configuration of the gate dielectric determines, in part, the strength of the electric field that a particular gate voltage will produce at the semiconductor channel. Some gate dielectrics have a configuration that causes a small change in gate voltage to produce a large change in the strength of the electric field applied to the active semiconductor channel. These gate structures have high sensitivities and are desirable in many FET applications.
One way to produce a high sensitivity gate structure involves making the gate dielectric from a very thin layer. Contemporary layers for gate dielectrics are rapidly approaching the minimum thickness for an electrical insulating layer. Thus, other ways for making a gate structure with a high sensitivity are desirable.
Various embodiments provide field-effect-transistors (FETs) in which a quasi-one-dimensional (1D) material functions as a gate dielectric. The quasi-1D material has a dielectric constant with a larger real part at low and moderate gate operating frequencies. The high value of the real part of the dielectric constant makes the gate structure ultra-sensitive. The new gate dielectric can be either a thin layer or a layer that is significantly thicker than conventional layers for gate dielectrics.
In one aspect, the invention features a field-effect transistor (FET) having a source electrode, a drain electrode, a gate electrode, a gate dielectric, and a semiconductor layer that functions as an active channel of the FET. The active channel is configured to carry a current between the source and drain electrodes and has a conductivity that is responsive to voltages applied to the gate electrode. The gate dielectric is located between the gate electrode and the semiconductor layer and includes a quasi-1D charge or spin density wave material.
In another aspect, the invention features a method of operating a field-effect transistor with a gate electrode, a source electrode, a drain electrode, and an active semiconductor channel. The method includes establishing a current flow in the active semiconductor channel by applying a voltage across the source and drain electrodes and changing the current flow by adjusting a voltage applied to the gate electrode. The adjusting a voltage step causes a change in the strength of an electric field in a charge or spin density wave material that is located between the channel and the gate electrode.